Unless otherwise indicated herein, the materials described in this section are not prior art to the claims and are not admitted to be prior art by inclusion in this section.
An aircraft typically includes a plurality of aircraft equipment inside an upper fuselage segment of the aircraft, such as various systems, equipment, furnishings, and linings. These various systems, equipment, furnishings, and linings may include, for example, electrical equipment, wires, environmental control system (ECS) equipment and ducts, oxygen lines, water lines, power feeders, cabin ceiling panels, and other items. Typically, one or more secondary structures attached to the airframe provide support for these various systems, equipment, furnishings, and linings inside the upper fuselage segment. In an example, a secondary support structure is provided for the cabin ceiling, another secondary support structure is provided for electrical equipment, and yet another secondary support structure is provided for the ECS equipment and ducts.
As another example, an existing solution includes a secondary structure in the form of grid and trusses and joists suspended on large tie rods. This structure is dubbed “the lattice” and is situated above the aircraft cabin ceiling. The lattice provides support to the equipment, furnishings, and linings above the cabin ceiling.
Although the lattice allows for both stable and variable configurations, the lattice is expensive, heavy, and difficult to install. The installation of the lattice in the aircraft and the attachment of equipment, furnishings, and linings to the lattice are primarily performed inside the aircraft. This attachment and installation process inside the aircraft is both time consuming and difficult. For example, this attachment and installation process typically involves numerous installation personnel, which may lead to congestion inside the aircraft during the installation process. This process is also time-consuming, as the process requires numerous installation steps and adjustments.
Existing secondary structure or structures can provide support for stable configurations of primary structures as well as variable configurations of payloads and systems. However, although existing secondary structure or structures can provide for variable configurations, often variable structural provisions on existing secondary structures remain underutilized. This underutilization adds additional weight to the support structure and also results in additional costs. There is, therefore, a need for a more cost-effective support structure and a less labor intensive method of assembling and installing a support structure for a crown portion of an aircraft.
Further, many system installation supports utilized in existing secondary support structures are supports composed of conventional sheet metal construction. Smaller scale sheet metal brackets and support trays are easy to manufacture and assemble, and they also provide conductivity for electric grounding and bonding. However, larger scale sheet metal trays and panels often used in wide-body aircraft require progressively more stiffening elements to provide adequate rigidity. This increases both the cost and weight of support structures. Composite honeycomb panels are often used for larger support panels. However, composite structures require specialized hardware to interface with attached equipment. Further, many composites are not electrically conductive and they require additional provisions for grounding and bonding. There is, therefore, a need for an improved system installation support for use in a secondary support structure or structures for a crown of aircraft.
Another drawback of existing secondary structures is that the process of attaching cabin ceiling panels to existing secondary structures and aligning the ceiling panels is difficult and time consuming. This existing process typically involves numerous steps, including repetitive tightening and loosening of fasteners, screwing and unscrewing tie rods, setting and resetting serrated pads, and the use of shimming. The process also often involves repetitive installation, removal, and re-installation of panels in order to obtain proper alignment of all of the panels. Thus, the existing process for attaching the ceiling panels to existing secondary structures is both time-consuming and costly. There is, therefore, a need for an improved system for attaching the ceiling panels to existing secondary structures and aligning the ceiling panels.
Yet another problem with existing secondary structures is adapting and adjusting to build tolerances that typically exist in airframes on an aircraft. Due to build tolerances from frame-to-frame, many existing structural attachments that attach directly to the airframe typically incorporate manual-adjustment features that compensate for build tolerances. For example, a secondary structure may be fastened to the airframe with tie rods, and these tie rods may be manually adjusted in order to accommodate for build variations in the airframe. These manual-adjustment features, however, introduce additional costs with not only additional parts but also additional labor. Further, these manual-adjustment features increase assembly time by adding additional steps to the assembly process. There is, therefore, a need for an improved system for attaching secondary structure to an airframe that accounts for build tolerances.